EVOLUTION OF A GENERALIST GENOTYPE - MULTIVARIATE-ANALYSIS OF THE ADAPTIVENESS OF PHENOTYPIC PLASTICITY

Phenotypic plasticity, whereby a single genotype produces alternative phenotypes in alternative environments, is often cited as a characteri stic of generalists: the alternative phenotypes allow the species to e xploit a broader range of environmental conditions. However, plasticit y may be adaptive or may simply result from developmental instability, Most recent work on the adaptiveness of plasticity has focused on ana lyses of single traits, whereas the alternative phenotypes are likely to involve alteration of a suite of characters. Multivariate analysis would allow separation of direct adaptive plasticity from what we term indirect adaptive plasticity. Predator-prey inducible defense systems , such as the interaction between larval Chaoborus americanus (an aqua tic dipteran ambush predator) and Daphnia pulex (a freshwater crustace an) provide excellent opportunities to evaluate the adaptiveness of pl asticity, This study was conducted to separate direct from indirect ad aptive induced change in Daphnia for morphological characters with res pect to the agent that causes the induced change: the presence of Chao borus. Of the eight characters assayed, four were found to independent ly contribute to the enhanced fitness exhibited by the induced morph. The differences between the interpretation of the data based on univar iate and multivariate analyses were marked, This underscores the impor tance of assessing tile adaptiveness of plasticity in a multivariate c ontext.